In recent years, with the continuous improvement of semiconductor design and manufacturing technology, image sensor chips are developed with more integrations and diversifications, in purpose of achieving more abundant functions and superior image sensing performance while ensuring ease of the implementation.
CMOS image sensor chip is a type of sensor chip that uses an active pixel sensing unit/element and is widely used in cameras, camera equipment, and the like because of its low power consumption and high operating speed.
FIG. 1 shows a conventional image forming apparatus (or system). The imaging device includes a CMOS image sensor chip 10 and a microcontroller unit (MCU)/image signal processor (ISP) chip 12. Both can be set on a printed circuit board (PCB). The CMOS image sensor chip 10 may sense image(s) and provide image signals to the MCU/ISP chip 12 for processing. The MCU/ISP chip 12 may control the entire system as a main controller of the system; therefore, the MCU/ISP chip 12 may also sometimes be referred to as a host computer chip of the CMOS image sensor chip 10.
The MCU/ISP chip 12 may receive the image signal transmitted from the CMOS image sensor chip 10 to perform image signal processing and provide the image to the display 18 for display. The MCU/ISP chip 12 may also send a control signal to the CMOS image sensor chip 10. The MCU/ISP chip 12 can also control other various drivers 16.
The imaging system may also include a photo-resistor 14 to detect ambient light. The MCU/ISP chip 12 can switch an infrared filter (IR-CUT) 20 according to the signal provided by the photo-resistor 14, and control the CMOS image sensor chip 10 so that the imaging system can switch between a color image mode and a black-and-white image mode. At the same time, the MCU/ISP chip 12 controls the light source (e.g., LED) 22 to compensate the light to improve the imaging quality.
For the system, additional discrete component for detecting light intensity (such as the photo-resistor CdS) and related board-level circuits to assist in the operation of the discrete components are incorporated, which leads to increased manufacturing costs and increased power consumption, and may bring about additional costs due to differentiations and complications of the system.
On the other hand, flicker of ambient light (e.g., flicker of light caused by utility-provided electric power at a frequency of 50 Hz/60 Hz, etc.) adversely affects the imaging quality. Although such flicker may be not a problem for the human eyes, it poses problems for the imaging of the image sensors, for example, rendering ripples in the formed images. In the prior art, a method of analyzing image data collected by a CMOS image sensor chip is generally used to detect the flicker. However, a disadvantage of such a conventional method is that it requires multiple frames of data for evaluation, and the amount of data to be processed is very huge, which greatly increases the workload of the host MCU/ISP chip, and also leads to more resource consumption. With the increase of the resolution of the image sensor chip, the amount of data to be processed in detecting of the flicker of the ambient light using the conventional method also increases significantly, thus the disadvantages of the conventional method becomes even more serious. In addition, the exposure time of the image sensing unit of the image sensor chip may be changed time to time, increasing the difficulty and complexity of the flicker detection.
Although in some chips of the prior art, the flicker detection function is integrated into the CMOS image sensor chip, the methods are basically similar, and multi-frames of data need to be processed. And thus, the foregoing problem(s) still exist. Such integration means that the circuit design is more complex and the overall cost is increased while the chip area is increased.
In addition, for ambient light intensity and ambient light flicker, the detections thereof are generally independent in conventional imaging systems, and the detections relying more on board-level discrete devices and host computer chips to achieve such functionalities. This may lead to inefficiency and high cost of detection.
Therefore, there is a need for improved image sensors and imaging devices.